The present invention relates to a prefetch and restore method and apparatus of a semiconductor memory device; particularly to a method and apparatus for, in a restore operation, driving a bit line sense amplifier after write data on a pair of global data bus lines is delivered to a pair of bit lines, so as to reduce a size of a driver used to invert a logic value of data sensed by the bit line sense amplifier when logic values of cell data and the write data are opposite in a restore operation and also decrease a power consumption and a noise.
In general, when a weak data signal stored in a cell of a memory cell array is provided onto a pair of bit lines BL and /BL, a bit line sense amplifier detects the weak data signal and amplifies the detected data signal into a power voltage Vcc or a ground voltage Vss according to a logic value of the detected data signal.
Hereinafter, there will be explained a prefetch (or read) and restore (or write) operation in such memory devices as a dynamic random access memory (DRAM), synchronous DRAM and DRAMs (CDRAM, EDRAM, VCM, and the like) employing a memory buffer therein.
First of all, in the read (or prefetch) operation, the data stored in the memory cell is coupled to a pair of transfer bus lines via the bit line sense amplifier and then temporarily stored in a channel buffer. The temporarily stored data is outputted to the outside of the memory device via a data output buffer and an output pad.
In the write (or restore) operation, the write data inputted through an input pad is temporarily stored in the channel buffer via a data input buffer and then stored in the memory cell through the pair of data bus lines and the pair of bit lines.
There will be explained in detail the read or prefetch operation reading out cell data stored in a memory cell.
If a row address is inputted to the inside of the memory device, a word line corresponding to the row address is activated and a corresponding cell data is retrieved onto a pair of bit lines BL and /BL by a charge distribution. Then, if control signals RTO and SB are enabled to drive a bit line sense amplifier, the bit line sense amplifier amplifies a weak data signal on the pair of bit lines BL and /BL into the power voltage Vcc or the ground voltage Vss according to a logic value of the data signal. The time required from the inputting of the row address to the sensing of the data signal is called as a row active time tRCD.
After the row address is inputted, if a column address is inputted, a pair of bit lines BL and /BL selected by the column address are connected to a pair of global data bus lines GDB and /GDB and, hence, the data on the pair of bit lines BL and /BL are transferred onto the pair of global data bus lines GDB and /GDB.
The data on the pair of global data bus lines are amplified by the data line sense amplifier and then outputted to the outside of the memory device via a corresponding data output buffer.
There will be explained in detail the write or restore operation writing data onto a memory cell.
If a row address is inputted to the inside of the memory device, a word line corresponding to the row address is activated and a corresponding cell data is fed onto a pair of bit lines BL and /BL by the charge distribution. Then, if control signals RTO and SB are enabled to drive a bit line sense amplifier, the bit line sense amplifier amplifies the weak data signal on the pair of bit lines BL and /BL into the power voltage Vcc or the ground voltage Vss according to a logic value of the data signal. The time required for the above process is referred to as the row active time tRCD.
After then, if the pair of bit lines BL and /BL selected by the column address are connected to a corresponding pair of global data bus lines GDB and /GDB, write data is delivered onto the pair of global data bus lines GDB and /GDB in response to an operation of a write driver. At this time, since the pair of global data bus lines and the pair of bit lines are connected to each other, the write data on the pair of global data bus lines are transferred onto the pair of bit lines. Accordingly, the write data on the pair of bit lines are stored in the memory cell.
Referring to FIG. 1, there is illustrated a schematic diagram of explaining a structure of a virtual channel memory (VCM).
As described in FIG. 1, the VCM comprises a multiplicity of cell array units 10 less than 0 greater than  to 10 less than N greater than  each of which includes a plurality of memory cells; pairs of bit lines BL and BLB for connecting the memory cells with bit line sense amplifying units 20 less than 0 greater than  to 20 less than N greater than ; the bit line sense amplifying units 20 less than 0 greater than  to 20 less than N greater than  for detecting and amplifying the data on the pairs of bit lines BL and BLB; pairs of transfer bus lines TB less than 0 greater than  to TB less than N greater than  and TBB less than 0 greater than  to TBB less than N greater than  for connecting the bit line sense amplifying units 20 less than 0 greater than  to 20 less than N greater than  to a channel buffering unit 30; transfer transistors N1 and N2, and N3 and N4 for switching, in response to a control signal TB_CTRL, data between the pairs of bit lines BL and BLB and the respective pairs of transfer bus lines TB less than 0 greater than  to TB less than N greater than  and TBB less than 0 greater than  to TBB less than N greater than ; the channel buffering unit 30 for storing the data provided through the pairs of transfer bus lines TB less than 0 greater than  to TB less than N greater than  and TBB less than 0 greater than  to TBB less than N greater than , or storing data provided from a read sense amplifier/write driver 40; the read sense amplifier/write driver 40 for accessing data from the channel buffering unit 30 or delivering data to the channel buffering unit 30; and an input/output (DQ) buffer/pad 50 for buffering data provided from the read sense amplifier 40 and outputting the data through an output pad, and buffering write data inputted through an input pad and transferring the write data to the write driver 40.
In the prefetch (or read) operation of the above VCM, if a certain word line is activated along with a row path generated by a prefetch instruction, data stored in all of cells connected to the certain word line are coupled onto their respective pairs of bit lines BL and BLB. Then, if the sense amplifier driving signals RTO and SB are enabled in response to a control signal SG, all of bit line sense amplifying units 20 less than 0 greater than  to 20 less than N greater than  corresponding to the pairs of bit lines BL and BLB are activated and the data on the pairs of bit lines BL and BLB are sensed into the power voltage Vcc or the ground voltage Vss.
The sensed data on the pairs of bit lines BL and BLB are temporarily stored in the channel buffering unit 30 via the transfer bus lines TB less than 0 greater than  to TB less than N greater than  and TBB less than 0 greater than  to TBB less than N greater than  and then amplified by the data bus line read sense amplifier 40 to thereby being outputted to the outside of the memory device through the DQ buffer/pad 50.
On the other hand, in the restore (or write) operation, write data are temporarily stored in the channel buffering unit 30 after being inputted via the input pad, the input buffer and the write driver in response to a write instruction. In order to store the temporarily stored data in the memory cells, a word line corresponding to the row path is actuated and, thereafter, the data stored in the memory cells are provided onto the pairs of bit lines BL and BLB by the charge distribution.
Referring to FIG. 2, there is shown a schematic diagram of explaining a process for generating conventional sense amplifier driving signals RTO and SB.
First of all, if a /RAS signal is enabled, a word line corresponding to an inputted row address is activated and then a sense amplifier driving signal generating circuit 22 is activated in response to a control signal SG to thereby produce the bit line sense amplifier driving signals RTO and SB.
Referring to FIG. 3, there is described a timing diagram of showing an activating order of a transfer bus line control signal TB_CTRL and sense amplifier driving signals RTO and SB in a prefetch operation.
As shown in FIG. 3, after a word line W/L is enabled, a pull-up bias voltage signal RTO and a pull-down voltage signal SB are generated to thereby drive the bit line sense amplifying units 20 less than 0 greater than  to 20 less than N greater than . Then, the control signal TB_CTRL is produced to thereby provide the pairs of transfer bus lines TB less than 0 greater than  to TB less than N greater than  and TBB less than 0 greater than  to TBB less than N greater than  with the data on the pairs of bit lines BL and BLB amplified by the bit line sense amplifying units 20 less than 0 greater than  to 20 less than N greater than . In response to the control signal TB_CTRL, the transfer transistors N1, N2, N3 and N4 are turned on and the amplified cell data on the pairs of bit lines BL and BLB are delivered onto the pairs of transfer bus lines TB less than 0 greater than  to TB less than N greater than  and TBB less than 0 greater than  to TBB less than N greater than .
In the conventional bit line sense amplifier control circuit, if data stored in a cell is identical to data to be written, there is no problem. However, if the above two data are different from each other, there may occur following problems.
That is, in the write or restore operation storing the data in the memory cell, since the row path is first actuated, a certain data of a cell is provided onto a pair of bit lines and then amplified by the sense amplifier into the power voltage Vcc or the ground voltage Vss. Then, as the column path is actuated, if the pair of bit lines is connected to the pair of global data bus lines, the write driver must invert a sensed opposite data. Therefore, a size of the write driver should be large enough to invertly operate the continuously operating bit line sense amplifier as well as inverting the opposite data on the pair of bit lines and the pair of global data bus lines. Further, in order to invert the opposite data, there needs a large amount of power consumption.
Moreover, the operation of the memory device may be entirely unstable due to a noise on a power line caused by the great power consumption.
Specifically, since dozens of or hundreds of bits of data are prefetched or restored in one operation in special DRAMs such as cache DRAM (CDRAM), VCD, enhance DRAM (EDRAM), enbaded frame (EF) buffer and multi-bank DRAM, the power consumption and the noise can be critical problems.
It is, therefore, an object of the present invention to provide a method and apparatus for, in a restore operation, driving a bit line sense amplifier after write data on a pair of global data bus lines is delivered to a pair of bit lines, so as to reduce a size of a driver used to invert a logic value of data sensed by the bit line sense amplifier when logic values of cell data and the write data are opposite in a restore operation and also decrease a power consumption and a noise.
In accordance with one aspect of the present invention, there is provided a method for pre fetching and restoring data stored in memory cells in a semiconductor memory device, comprising the steps of: a) performing a pre fetching operation, the pre fetching operation including the steps of:
applying the data onto pairs of bit lines after a specific word line is activated by a row path; sensing the data applied on the pairs of bit lines by bit line sense amplifiers driven in response to an enabled bit line sense amplifier driving signal; and transferring the data applied on the pairs of bit lines to pairs of global data bus lines in response to a control signal for connecting the pairs of bit lines with the pairs of global data bus lines, and b) performing a restoring operation, the restoring operation including the steps of: applying the data on the pairs of bit lines when the specific word line is activated by the row path; applying write data on the pairs of global data bus lines; transferring the write data applied on the pairs of global data bus lines to the pairs of bit lines in response to the control signal; and sensing the write data applied on the pairs of bit lines by the bit line sense amplifiers to store sensed write data into the memory cells.
In accordance with another aspect of the present invention, there is a provided an apparatus for pre fetching and restoring data stored in memory cells in a semiconductor memory device having a memory buffer, comprising: a bit line sense amplifying means for sensing the data stored in the memory cells in response to a bit line sense amplifier driving signal; and a control means for driving the bit line sense amplifying means before data applied on pairs of bit lines are transferred to pairs of data bus lines in response to a control signal during a pre fetching operation, and for driving the bit line sense amplifying means after data applied on the pairs of bit lines via the pairs of data bus lines is transferred to the pairs of bit lines in response to the control signal.